After Scott Brown defeated Democrat Martha Coakley, a poll found that a whopping 49 percent of union voters had bucked their leadership to go with the Republican.

There are a few reasons so many union members took to Brown. The Wrentham Republican had voted with labor about 80 percent of the time in the state Senate, where he sought and won the AFL-CIO’s endorsement. He presented himself as a regular guy with a truck, just like a lot of them. And union leadership, like most Democrats, took victory for granted until it was too late.

Since he took it over a year ago, Tolman has been trying to expand the AFL-CIO, bringing teachers, restaurant workers, and state employees back into the organization. But growing membership is meaningless unless labor can be marshaled to a cause.

This Senate election will show if the AFL-CIO has its electoral oomph back.

“It’s my goal to [help] members . . . make a better-informed decision than they did in 2010,” Tolman says. “One of the problems we keep finding is that people believe things that aren’t true about [Brown].”

The union is making a mammoth effort on behalf of Elizabeth Warren. Hundreds of union types have been knocking on doors each weekend to spread the word. Tolman says an additional 1,000 will go out this weekend. They’ve been working job sites, phone banks, and social media, hammering Brown for voting with labor only about 20 percent of the time in ­Washington. They cite one of Brown’s first votes, against a nominee to head the ­National Labor Relations Board viewed by Republicans as too friendly to unions; Brown’s votes against several jobs bills; and his willingness to hold up extensions to unemployment insurance to extract concessions on other issues, such as tax cuts. (Brown’s campaign did not return messages, but in the past has claimed he opposed these measures because he wanted them paid for in ways that didn’t increase the deficit.)

Tolman points to the fact that, after he met with Brown at Victoria’s Diner in ­Boston earlier this year and told him labor would look hard at his record, Brown made no effort to win AFL-CIO support, failing to complete a questionnaire. Not to rub salt and all that, but Brown didn’t complete it in 2010 either, and it didn’t hurt him.

Polls show Brown holds a giant lead among white men in this race, a demographic that makes up more than half of the AFL-CIO’s 400,000 members. Drawing them away from the Republican is no gimme. Still, Tolman is optimistic that they’ll come back once they see beyond Brown’s pickup truck to his record.

The scene at a Seaport coffee shop yesterday morning would have warmed the union leader’s heart. A dozen burly steelworkers sat around tables, taking a break from a job. All said they were voting for Warren. Most said they’d gone for Coakley in 2010, but one worker, who declined to give his name, had voted for Brown.

“He’s from down my way,” said the worker, a tall 44-year-old. “I voted for him because I thought he’d improve the economy and bring a new outlook. That didn’t work.”

He’s a natural Republican voter in some ways, the steelworker said. He has other sources of income, and little patience for welfare. But he can’t get past the fact that Brown voted against extending unemployment insurance his friends needed.

“God forbid that was me, with three kids,” the worker said, pulling on a green hoodie and heading back to work. “I don’t see a lot of compassion there.”

A Warren victory could depend on guys like this. The political credibility of the Massachusetts AFL-CIO certainly does.